Use the Messages base URL
The Anthropic SDK appends /v1/messages, so its base URL is https://formalengines.com/inference. This differs from the OpenAI SDK base URL, which ends in /v1. The gateway requires Authorization: Bearer; an x-api-key header alone does not authenticate. Configure the Anthropic Python SDK with auth_token=os.environ["ANTHROPIC_AUTH_TOKEN"], or use a client that supports Bearer authentication.
export ANTHROPIC_BASE_URL="https://formalengines.com/inference"
export ANTHROPIC_AUTH_TOKEN="YOUR_API_KEY"curl --fail-with-body https://formalengines.com/inference/v1/messages \
-H "Authorization: Bearer $ANTHROPIC_AUTH_TOKEN" \
-H 'anthropic-version: 2023-06-01' \
-H 'Content-Type: application/json' \
-d '{"model":"deepseek-v4-1-flash","max_tokens":256,"messages":[{"role":"user","content":"Hello."}]}'Protocol compatibility
Messages and Chat Completions use different response shapes and streaming events. Parse a Messages response with an Anthropic-compatible client rather than the OpenAI streaming parser. Availability, tool support, and provider-specific features depend on the selected model and route.
For a client that accepts only an OpenAI-compatible endpoint, use the OpenAI quickstart instead. Neither protocol requires you to use a provider-branded model ID; use the IDs from our catalog.